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CVE-2026-77550 – Authentication Bypass via CRLF Injection – Ubiquiti UniFi OS Server and Related Uni

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Summary

CVE-2026-77550 is a critical improper neutralization of CRLF sequences (CRLF injection, CWE-93) vulnerability affecting devices and software running Ubiquiti UniFi OS, including UniFi OS Server. A network-based attacker can exploit the flaw to bypass authentication on affected UniFi OS devices or instances without any privileges or user interaction. The vulnerability carries a maximum CVSS v3.1 base score of 10.0 and was disclosed by Ubiquiti in Security Advisory Bulletin 067.

Technical details

  • Root cause: improper neutralization of CR/LF sequences (CWE-93) within UniFi OS request/response handling.
  • Trigger conditions: no authentication or user interaction required; low attack complexity.
  • Attack vector: network-based, exploitable remotely against any exposed UniFi OS instance.
  • Impact: complete authentication bypass on the affected UniFi OS device or instance, enabling unauthorized access to management functions.

Affected software

  • UniFi OS Server: versions prior to 5.1.37
  • Cloud Keys: versions prior to 5.1.31
  • Network Video Recorders: versions prior to 5.1.31
  • Enterprise Network Video Recorders: versions prior to 5.1.31
  • Enterprise Network Attached Storage: versions prior to 5.1.31
  • Dream Machines: versions prior to 5.1.31
  • Enterprise Firewall Core: versions prior to 5.1.31
  • Dream Routers: versions prior to 5.1.31
  • Enterprise Fortress Gateway: versions prior to 5.1.31
  • Cloud Gateways: versions prior to 5.1.31
  • Dream Wall: versions prior to 5.1.31
  • Express 7: versions prior to 5.1.31
  • Network Attached Storage: versions prior to 5.1.32
  • Express: versions prior to 4.0.17

Severity

CVSS v3.1 Base Score: 10.0 (Critical)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade affected products to the patched versions specified by Ubiquiti — UniFi OS Server to 5.1.37 or later, most Cloud Key/NVR/Gateway/Dream Machine product lines to 5.1.31 or later, Network Attached Storage to 5.1.32 or later, and Express appliances to 4.0.17 or later.
  • If immediate patching is not possible: Restrict network exposure of UniFi OS management interfaces to trusted networks only, and remove direct internet exposure of UniFi OS Server/console login and management endpoints until patched.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Page title: UniFi OS

References

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Map your entire attack surface (continously)

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4

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IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

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